1. Field of the Invention
The present invention relates to an aluminum electrolytic capacitor having external terminals for use in various kinds of electronic equipment and to a method of manufacturing the capacitor.
2. Background Art
FIG. 5 is a sectional view illustrating a structure of a conventional aluminum electrolytic capacitor. FIG. 6 is a sectional view of an essential part of the conventional capacitor. FIG. 7 is a sectional view of an essential part of the conventional capacitor before a rivet thereof is upset. Capacitor element 10 shown in FIGS. 5 through 7 is structured so that a positive electrode foil (not shown) and a negative electrode foil (not shown) are rolled, sandwiching a separator (not shown) therebetween. The positive electrode foil has dielectric surface oxide layers formed by anodizing an aluminum foil having roughened surfaces. The negative electrode foil is made of an aluminum foil having roughened surfaces.
The method of assembling a conventional aluminum electrolytic capacitor is outlined hereinafter. A conventional aluminum electrolytic capacitor includes aluminum internal leads 11, i.e. one connected to the positive electrode foil at one end and the other to the negative electrode foil at one end, terminal plate 12, a pair of external terminals 13 provided on this terminal plate 12, aluminum rivets 14, and aluminum spacers 15. In a manufacturing process, external terminals 13 are fixed to terminal plate 12 by corresponding aluminum rivets 14. At the same time, the tip portion of each aluminum rivet 14 penetrating through this terminal plate 12 and projecting therefrom is threaded through through-hole 110 previously provided at the other end of each of internal leads 11, via spacer 15. After another spacer 15 is further fitted on the rivet, the tip portion of aluminum rivet 14 projecting from the other spacer 15 is upset. With these steps, internal leads 11 and corresponding external terminals 13 are electrically connected with each other. Through-hole 110 previously provided at the other end of each internal lead 11 is formed to have opening diameter xcfx86C slightly larger than outer diameter xcfx86D of aluminum rivet 14, in consideration of workability.
Further, this capacitor element 10 and an electrolyte solution (not shown) are contained in cylindrical metal case 16 having a bottom. Attached to the outer peripheral surface of this metal case 16 is resin sleeve 161 made of vinyl chloride. At last, the periphery of the opening of this metal case 16 is drawn so as to surround this terminal plate 12, to seal the metal case. Thus, an aluminum electrolytic capacitor having a pair of external terminals 13 is constructed.
In a conventional aluminum electrolytic capacitor, a pair of internal leads 11 drawn from capacitor element 10 are electrically connected to a pair of external terminals 13 provided on terminal plate 12 by threading corresponding through-holes 110 provided at the other ends of internal leads 11 with aluminum rivets 14 and then upsetting the tip portions of aluminum rivets 14. At this time, each of through-holes 110 is formed to have opening diameter xcfx86C slightly larger then outer diameter xcfx86D of aluminum rivet 14, in consideration of workability. For this reason, connection between internal lead 11 and external terminal 13 depends on the contact between aluminum rivet 14 and the flat portion of internal lead 11 or part of through-hole 110 where aluminum is exposed by punching.
However, internal lead 11 connected to the positive electrode foil has dielectric oxide layers formed on the surfaces thereof by anodic oxidation. This has posed an inherent drawback: even when the surfaces of internal lead 11 are in contact with aluminum spacers 15, it is difficult to provide electrical connection therebetween. Additionally, as an aluminum electrolytic capacitor continues to be used, the electrolyte solution entering into through-holes 110 having exposed aluminum surfaces chemically reacts with the aluminum and the reaction produces oxide layers on the exposed aluminum surfaces. As a result, it becomes more difficult to provide electrical connection. This has posed a problem of malfunction caused by contact failure.
The present invention addresses these conventional problems and aims to provide a reliable aluminum electrolytic capacitor in which electrical connection between internal leads and external terminals are ensured.
In order to attain these objects, an aluminum electrolytic capacitor of the present invention includes: (a) a capacitor element structured so that a positive electrode foil and a negative electrode foil are rolled, sandwiching a separator therebetween, (b) internal leads, i.e. one connected to the positive electrode foil at one end and the other to the negative electrode foil at one end, (c) a cylindrical metal case having a bottom for containing this capacitor element together with a electrolyte solution, (d) a pair of external terminals each coupled to the other end of one of the internal leads, and (e) a terminal plate disposed in an opening of the metal case and sealing the metal case. The other end of each of the internal leads has a through-hole. Provided around the peripheral edge of this through-hole is a cylindrical portion formed integral with the internal lead by drawing. While this cylindrical portion is threaded with an aluminum rivet for fixation of the external terminal and the inner peripheral surface of the cylindrical portion is in contact with the outer peripheral surface of the aluminum rivet, the tip portion of the aluminum rivet is upset. Thus, the external terminals provided on the terminal plate are electrically connected to the corresponding internal leads.
In a method of manufacturing an aluminum electrolytic capacitor of the present invention, a punch having a smaller diameter part at its tip, and a dice having a hole for receiving the smaller diameter part therein are used. By lowering the punch, a prepared hole is drilled at one end of each of aluminum internal leads connected to the positive electrode foil or the negative electrode foil. By successively lowering the punch, the prepared hole is drawn to form a cylindrical portion integral with the prepared hole.
Additional objects and advantages of the present invention will be apparent from the following detailed description of a preferred embodiment thereof, which is best understood with reference to the accompanying drawings.